Journal of cell science
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Journal of cell science · Sep 2003
Rat aorta-derived mural precursor cells express the Tie2 receptor and respond directly to stimulation by angiopoietins.
Recent studies have implicated the Tie2 tyrosine-kinase receptor and its main ligands--angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2)--as crucial regulators of mural cell recruitment during angiogenesis. Angiopoietin-mediated activation of Tie2 promotes perivascular mural cell assembly, but the mechanisms regulating this process are poorly understood because differentiated mural cells do not have the Tie2 receptor, which is reportedly expressed only in endothelial cells. There is also no direct evidence that Tie2 activation results in production of mural cell chemoattractants by the endothelium. ⋯ Surface expression of Tie2 was further demonstrated by isolating Tie2+/alpha-smooth muscle actin+ MPCs from primary aortic outgrowths with anti-Tie2-IgG-coated magnetic beads. Immunostaining of the rat aorta confirmed expression of Tie2 not only in endothelial cells but also in nonendothelial mesenchymal cells located in the aortic intimal/subintimal layers, which are the source of MPCs. These data indicate that the aortic wall contains Tie2+ nonendothelial mesenchymal cells and suggest that Tie2-related recruitment of mural cells during angiogenesis may occur through angiopoietin-mediated direct stimulation of these cells.